Soil acidity
17
COMBINE
CULTIVATION
AND LIME
TO RAPIDLY
LIFT YIELDS
By Chris Gazey and Liam Ryan
WHEN DEEP RIPPING, ploughing or
spading to remove subsurface compaction
or other soil constraints it can pay
to also incorporate lime to depth.
Recent research in Western Australia,
where subsoil acidity is a problem,
shows incorporating lime into the soil
via mouldboard ploughing or rotary
spading can ameliorate subsoil acidity
at least two to three years faster than if
lime was top-dressed. Deep incorporation
of lime is likely to work best where
subsoil acidity occurs in a distinct layer,
typically between 15 and 35 centimetres,
rather than down the whole profile.
It is best to spread lime on the
surface before deep ripping, ploughing
SOIL-MIXING CALCULATOR
Researchers in Western Australia are using a new method to
quantify the degree to which different tillage implements mix soil (and
therefore applied lime). Trials of the new method in 2014 showed
soil inversion with a mouldboard plough, rotary spader and one-
way plough created equally patchy soil. Further soil mixing work is
being undertaken in 2015 to help develop a model to predict the
redistribution of soil layers and ameliorants (such as lime) using
different implements. A soil-mixing calculator is targeted for release at
the 2016 Perth Crop updates.
FIGURE 1
Lime incorporation pattern (purple indicates
high-pH soil) using a spader.
PHOTOS: JOEL ANDREW, PRECISION SOILTECH
FIGURE 2
Lime incorporation pattern using a mouldboard
plough (low pH is shown as orange and higher
pH as green/purple).
FIGURE 3
Samples of soil from a depth of one metre from
a spaded (dry soil, bottom) and unspaded (wet
soil, top) demonstration section of the same
paddock.
SOURCE: DAFWA
Wheat grain yield (t/ha)
1.6
1.2
0.8
0.4
0
FIGURE 4 Wheat yields of
a spaded and unspaded
section of a paddock in an
on-farm spading demonstration
at Mingenew, Western Australia.
Post-liming treatment
Not spaded
Spaded
Two tonnes per hectare of
quality lime delivered an
average 0.25t/ha or 12 per cent
increase in wheat yields across
100 lime-response trials in
Western Australia.
or spading as this enables better
distribution of the lime particles and
greater contact with the acidic soil.
Rotary spading generally achieves a
better distribution of lime through the
soil profile than mouldboard ploughing,
which tends to bury the lime with
the topsoil, leaving an acidic layer
on the surface (Figures 1 and 2).
In the spading demonstration depicted
in Figure 1, crop roots were present to a
depth of 40 to 50cm, while in the unspaded
profile roots were present only to a depth
of 20 to 25cm. This was reflected in the
soil moisture profiles of the two treatments,
with soil samples showing the spaded
profile was drier (more water extracted
by crop roots) than the unspaded profile
to more than one metre (Figure 3).
Wheat yields were also higher in the
spaded treatment (Figure 4), with the
extra 0.7 tonnes per hectare of grain yield
sufficient to pay for the spading and
liming costs in the year of application. □
GRDC Research Code DAW00236
Caring for Country code SP11-01226
More information: Liam Ryan, DAFWA,
08 9622 1902, liam.ryan@agric.wa.gov.au